Light emitting diodes (LEDs) are devices that use a semiconductor diode that emits light when charged with electricity. LEDs provide light in a wide array of electronic devices. For example, LEDs are used as on/off indicators in electronic devices, are used to provide LCD or keypad backlighting in handheld devices, such as personal digital assistants (PDAs) and cellular telephones, and are used for digital display readouts, such as electronic signs. Typically, LEDs are manufactured into an electronic chip (e.g., LED chips) that provide for easy integration into electronic devices.
Moreover, LEDs have found their way into lighting applications, photo-therapeutic applications, and other applications where a compact, low voltage, rugged, and high efficiency light source is advantageous. In many such applications, a number of LEDs are arranged into an array or other pre-determined arrangement having similar or dissimilar LED types.
However, one problem associated with LED illumination array in a phototherapy context is the surface mount of the LED with respect to the substrate. That is, the LED or light source is mounted on top of the flexible substrate and the connections (including wiring, solders, etc.) for the light source are also on top of the flexible substrate.
FIG. 1 illustrates one prior art embodiment that has a substrate 10, an LED 12, and an interface comprising a solid layer 14 of light-diffusing and heat-insulating material. One example of material for the layer 14 is silicone having glass bubbles distributed randomly throughout. Another example of material for the layer 14 is silicone having Titania distributed throughout. Alternatively, or in addition, the layer 14 may be silicone having a matte finish on the skin contact surface 16. The skin contact surface may have a pattern, for example, a printed pattern, effective to scatter and diffuse light.
The backing comprises a solid layer 18 of light-reflective, heat-conductive material including a solid layer of light-diffusive, heat-conductive material. In addition, the backing includes a back cover spaced from a substrate 10 with a secondary spacer having gaps or channels therein directly across the substrate 10 from each of the LEDs 12. The backing also includes a back cover 24 spaced from the substrate 10 with a secondary spacer 25. In this case, the secondary spacer 25 is provided directly underneath each of the LEDs 12, and preferably is made of a highly heat conductive material. Heat thus flows from the LED 12 through the substrate 10 to the secondary spacer 25, which is cooled on either side by the gaps 26.
In the surface mount configuration, a silicone (or other insulating) coating 14 is necessary to stop any fluids or contaminants from contacting the surface of the flexible substrate and having deleterious effects on the circuitry and/or the light source mounted on the substrate surface. Additionally, in the surface mount configuration, the dissipation of heat from the light source can be extremely difficult thereby resulting in a decrease in the light producing capabilities of the light source to ensure that a user is not burned.